The Linux kernel's Intel VT-d PASID table entry replacement had a race condition vulnerability (CVE-2026-45945) due to updating a 512-bit PASID entry with a single structure assignment while the entry was active. Because hardware fetches the entry in multiple 128-bit chunks, this could cause torn reads, resulting in inconsistent IOMMU states and unpredictable faults. The fix removes unsafe replace helpers and uses a clear-then-update flow that clears the Present bit and completes an invalidation handshake before applying the new configuration, preventing torn reads and race conditions.

If exploited, this vulnerability could cause the IOMMU hardware to observe inconsistent PASID entry states, potentially leading to unpredictable behavior, spurious faults, and compromise of system integrity or availability. The CVSS 3.1 score is 8.8 (High), indicating significant confidentiality, integrity, and availability impacts. No known exploits have been reported in the wild.

A fix is available that changes the PASID entry update method to a clear-then-update flow, ensuring safe replacement without torn reads. Users should apply the official Linux kernel updates that include this fix. Since this affects Linux kernel versions used in various Ubuntu LTS releases, consult the respective vendor advisories for patched kernel versions and update accordingly. Patch status is not explicitly confirmed here; check vendor advisories for current remediation guidance.